Direct current (DC) power generation systems are used in many applications to provide DC power to a load. Typical DC power generation systems include a generator that produces an alternating current (AC) power output in response to an excitation and a rectifier to rectify the AC power output to a DC power output. A typical generator includes a rotor having two or more rotor poles and a stator surrounding the rotor. Each rotor pole includes a corresponding field winding, which produces a magnetic field when the rotor is rotated. The stator includes armature or stator windings in which an AC voltage is generated in response to the magnetic field produced by the rotating rotor. The stator windings may include one or more phase windings (e.g., single phase, three-phase, etc.). In many commercial applications, the generator is designed as a synchronous generator in which the frequency of the AC output is synchronized with the rotational speed of the rotor.
In synchronous generators, overall generator torque is based on the flux distribution of the air gap between the rotor and stator. The air gap flux distribution is generated based on the magnetic interaction between the field windings of the rotor and the armature windings of the stator. Fluctuations in the air gap flux can be caused by sudden changes in a load of a synchronous generator (e.g., a short circuit), which result in oscillations in the output of the generator. To alleviate the air gap flux fluctuations, typical synchronous generators include damper windings on each rotor pole of the rotor. During operation, a current is induced in the damper windings, which causes a cancellation magnetic field to be produced to reduce the fluctuations of the air gap flux and any torque pulsations. However, due to the cancellation magnetic field, the stator main flux transfers through the side of each rotor pole, which reduces the direct-quadrature (dq) axis reactance and can result in high short circuit current during the initial stage of a fault event (e.g., a short circuit).